1. Field of the Invention
This invention relates to an endoscope apparatus and to a method of controlling the operation thereof.
2. Description of the Related Art
An endoscope apparatus has an ordinary-light observation mode and a fluorescent observation mode. Until the tip of a fiber scope of the endoscope apparatus reaches the vicinity of internal tissue (an object of interest) deemed to be the affected area, the internal tissue is imaged while it is irradiated with white light in the ordinary-light observation mode. When the tip of the fiber scope reaches the vicinity of the internal tissue deemed to be the affected area, the internal tissue is irradiated with excitation light. The pigment of the internal tissue responds by emitting fluorescence, the image of the internal tissue is sensed by a solid-state electronic image sensing device, and image data representing the internal tissue is obtained. A diagnosis is made based upon the image of the internal tissue represented by the obtained image data.
A solid-state electronic image sensing device produces an output (dark current) even when light is not impinging upon it. For this reason the dark current is measured and a correction (dark-current correction) is applied to subtract the value of the dark current from the value of the output of the solid-state electronic image sensing device that prevails when light is incident upon the solid-state electronic image sensing device. The dark-current correction is carried out as follows:
In a first method, the solid-state electronic image sensing device is shielded from light and the dark current is measured before the fiber scope of the endoscope apparatus is inserted into the body of the patient. Data ascribable to the dark current is subtracted from image data obtained by sensing the internal tissue of the patient.
A problem, however, is that the dark current varies in dependence upon the temperature of the solid-state electronic image sensing device. An accurate dark-current correction cannot be made because there is a temperature difference between the temperature of the solid-state electronic image sensing device, which is located at the tip of the fiber scope, when it is inside the body of the patient and the temperature thereof when it is outside the body of the patient (the temperature inside the body of the patient is higher).
In a second method, the fiber scope of the endoscope apparatus is inserted into the body of the patient and data obtained from an optical black region of the solid-state electronic image sensing device at the tip of the fiber scope while the internal tissue is being illuminated is regarded as data indicative of the dark current. Data obtained from the optical black region is subtracted from the image data acquired by imaging the internal tissue.
Though the optical black area is shielded from light by a film of vacuum-deposited aluminum or the like, perfect shielding is difficult. Consequently, there are occasions where an accurate dark-current correction cannot be performed.
Accordingly, an object of the present invention is to perform a comparatively accurate dark-current correction in an endoscope apparatus.
According to the present invention, the foregoing object is attained by providing an endoscope apparatus comprising: a light source for emitting first light having a first wavelength characteristic in a first observation mode and emitting second light having a second wavelength characteristic in a second observation mode; an image sensing device for outputting image data representing an object of interest in an area illuminated by light emitted from the light source; a controller for controlling the light source so as to halt emission of light when there is a mode changeover between the first and second observation modes; and a correction device for correcting image data, which is output from the image sensing device and represents the image of the object of interest that was illuminated by at least one of the first light and second light, after the light emission is halted, using data output from the image sensing device when the emission of light from the light source is halted by the controller.
The present invention also provides a control method suited to the above-described endoscope apparatus. Specifically, the present invention provides a method of controlling an endoscope apparatus having a light source for emitting first light having a first wavelength characteristic in a first observation mode and emitting second light having a second wavelength characteristic in a second observation mode, and an image sensing device for outputting image data representing an object of interest in an area illuminated by light emitted from the light source, the method comprising the steps of: controlling the light source so as to halt emission of light when there is a mode changeover between the first and second observation modes; and correcting image data, which is output from the image sensing device and represents the image of the object of interest that was illuminated by at least one of the first light and second light, after the emission of light is halted, using data output from the image sensing device when the emission of light from the light source is halted.
In accordance with the present invention, the image sensing device is inserted into the body, first light having a first wavelength characteristic is emitted in a first observation mode and second light having a second wavelength characteristic is emitted in a second observation mode, thereby illuminating the object of interest (a patient""s internal tissue). The emission of light from the light source is halted when a changeover is made between the first and second observation modes.
When the emission of light from the light source is halted, the image sensing device outputs data (dark-current data output from the solid-state electronic image sensing device owing to dark current). By using the data obtained when the light emission from the light source is halted, a correction (dark-current correction) is applied to image data (inclusive of image data obtained periodically by movie photography and image data obtained by still-picture photography) representing the image of the object of interest that was illuminated by at least one of the first and second light.
Thus, dark current is obtained from the solid-state electronic image sensing device when the device has been inserted into the body. Image data representing the image of the internal tissue that was obtained by sensing the image of the illuminated object of interest is corrected using the obtained dark current.
Since both the data representing the dark current and the image data to be corrected are obtained when the image sensing device is inside the body, there is little variation in temperature. This makes it possible to eliminate the effects of temperature fluctuation. Further, since illumination is halted when the dark current is obtained, a comparatively accurate dark current can be obtained. (Since the image sensing device is inside the body, the device is shielded from light almost perfectly when illumination is halted.) As a result, a comparatively accurate dark-current correction can be achieved.
It is preferred that the image data corrected by the correction device be image data of the object of interest illuminated by the light source immediately after halting of the light emission.
Since the dark-current correction is carried out using dark current obtained immediately prior to imaging of the object of interest illuminated by the first and second light, a more accurate correction can be applied.
The controller may control the light source so as to halt the emission of light every time there is a mode changeover between the first and second observation modes. In this case, the correction device would correct the image data, which is output from the image sensing device and represents the image of the object of interest that was illuminated by at least one of the first light and second light, immediately after the emission of light is halted every time the emission of light is halted, using image data output from the image sensing device and representing the image of the subject every time the emission of light from the light source is halted by the controller.
Thus, a correction can be applied using dark current obtained immediately before every changeover between the first and second observation modes.
By way of example, the first light of the light source is visible light and the second light is excitation light for obtaining a fluorescent image of internal tissue. The second light may be near infrared light.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.